The present invention relates to improvements in downhole production pumps and operating systems therefor for use in pumping fluids from boreholes and especially an oil well production system for stripper wells wherein crude oil is removed from the borehole as fast as it comes into the well.
Marginal oil wells, also called stripper wells, are usually uneconomical for the major oil companies to operate because the labor and pumping costs are close to the revenue from the hydrocarbon sales. Every day many of these unprofitable stripper wells are being shut in, plugged, and abandoned. But there is a type of oil field hand that loves to get possession of these marginal wells because he has the where-with-all to scrounge up enough equipment to maintain and operate these wells at a small profit.
Many of these stripper wells in the U.S.A. produce only about 10 barrels or less, of hydrocarbons/day. These wells are important to the U.S. economy, especially during times of political unrest when they become vital to our national defense. After all, just one days production at a rate of 10 barrels, or 440 gal, of oil/day will operate a small auto several thousand miles after the crude oil has been refined into fuel.
Accordingly, it is desirable to make available novel oil well production equipment that is relatively inexpensive and can be assembled from mostly commercially available material and thereby increase the profit gleaned from a stripper well. Additionally, the novel equipment should be easy to work on and have low cost maintenance and operation. Further, the novel equipment should operate the well in such a manner that the production rate can be increased from marginal to profitable. When all of these and several other desirable attributes are considered, it is easy to see that they add up to a novel well production system that provides the unexpected result of changing an unprofitable situation into one that is profitable.
Most oil wells in West Texas are produced by a pump-jack unit that reciprocates a bottom hole pump. The pump-jack usually operates cyclically for time intervals selected to avoid reaching a pump-off condition which starts a destructive condition known as fluid pounding, or gas lock. This situation is evidenced by the hundreds of issued US Patents which address this problem. One simply never pumps-off a well.
Fluid pounding is encountered when a pump-off condition is reached due to the attempt to remove downhole fluid from the borehole faster than it can accumulate. This introduces compressible gas into the variable chamber of the downhole pump, causing the plunger to accelerate and xe2x80x9cpoundxe2x80x9d the bottom of the pump as the liquid supported by the plunger impacts the stationary valve assembly at the bottom of the pump barrel. Fluid pounding is destructive for it can result in accelerated wear and tear on the entire production equipment. Therefore, in most reciprocating downhole production pumps, a lot of consideration is given to avoiding a pump-off condition of the downhole pump.
Contrary to the prior art method of producing a well, the production system of the present invention is operated in a continually pumped-off condition by removing the formation fluid from the bottom of the well just as fast as it enters through the casing perforations of the borehole, thereby reducing the hydrostatic pressure against the pay zone to a minimum. This allows the oil bearing formation to produce at its maximum, but at the same time it is bound to ingest compressible gas into the bottom of the pump barrel, where it would be expected to cause fluid pounding, especially if provision is not made to avoid this occurrence. Accordingly, a purpose of this invention is the provision of a novel downhole pump and system that can accommodate the pumping of mixed hydrocarbon fluids (gas and liquid) and thereby change the problem of encountering a pump-off condition into an asset, while avoiding the dangers of fluid pounding. This is achieved in accordance with the present invention by the provision of a downhole pump assembly having a very long barrel that lifts both gas and liquid uphole every up-stroke of the pump plunger so that the pump chamber does not accumulate compressible fluids therewithin, but instead exhausts all gases along with the liquid each upstroke of the pump.
In addition to avoiding fluid pounding, this novel feature of this invention also has the unexpected advantage of enhancing pumping efficiency by using the gas expelled from the pump into the production tubing to provide additional lifting power in the manner similar to a well that uses a gas or air lift to produce liquid therefrom. Hence, gas that flows into the pump apparatus of this disclosure is slowly exhausted from the top of the variable chamber each upstroke of the pump plunger, and consequently there is no means by which the gas from a previous stroke can accumulate in the pump barrel for another stroke because the gas is removed from the pump apparatus at the end of each upstroke. Accordingly, fluid pounding is never encountered.
Further, the exceedingly long stroking pump plunger, together with the unusually slow time interval of the upstroke each cycle of operation, provides the necessary time delay for any gas that flows into the pump chamber to separate from the fluid and accumulate at the top of the barrel. During the slow plunger up-stroke the accumulated gas is slowly expelled from the pump variable chamber and enters the bottom of the production string at a very slow rate, which reduces the density of the contents of the tubing.
During the upstroke, the slow traveling pump plunger is acting against a constant lifting force and therefore does not accelerate significantly due to the differences in design between the system of this invention and the prior art production pumps, as will be more fully appreciated later on as this disclosure is more fully digested. Stated differently, there is not enough plunger speed and built-in inertia force in the present system as compared to the massive rotating parts of a prior art pumpjack operation to effect fluid pounding. Further, the low pumping speed of this novel cyclic operation along with the low bottom hole pressure at the perforations prevents accumulation of gases within the pump barrel for more than one cycle of operation, and this is a situation in which fluid pounding cannot be brought about.
Another novel feature of this disclosure is the provision of a method which reduces the oil/water ratio to a minimum by skimming the oil from above the oil/water interface of the formation fluid accumulated in the bottom of the well. The amount of water produced can be reduced until the desired crude production is achieved, or the desired oil/water ratio is achieved.
Other advantages of this disclosure over rod type downhole pumps is that the downhole production pump apparatus claimed herein can be pulled from the tubing by using the operating cable for reeling the lifting cable uphole until the pump apparatus surfaces. Then the entire pump apparatus can be serviced, as required, with change out of desired parts, and thereafter run back downhole into the borehole by unspooling the cable. Both method and apparatus that achieves the above desirable results are the subject of this invention and for which patent protection is sought.
In the prior art, it is noted that Coberly, U.S. Pat. No. 1,970,596, discloses a cable actuated long stroke pumping mechanism having a cable drum that includes a mechanical speed and switching control means associated therewith. The cable drum is rotated such that it accelerates the rate of travel of the plunger at the end of each stroke.
Mayer, et al, U.S. Pat. No. 4,761,120, measures a load on the rod string to provide automatic shutdown of a pumping unit.
London, et al, U.S. Pat. No. 5,372,482, controls the filling of a well pumping device by an arrangement in which the motor current is measured and compared to rod position using a computer to process the signals.
McKee, U.S. Pat. No. 4,973,226 discloses a pumpjack reciprocating a sucker rod string for actuating a downhole pump by measuring load on the rod string during a downstroke position of the walking beam to provide a signal which is stored and processed by a computer to determine the filling of a pump barrel. The electrical power to the pump jack motor is controlled by the computer to control stroke speed which keeps the pump barrel full by comparing instantaneous computer generated data with previous data and to continuously correct the filling of the barrel.
Improvements in downhole production pumps and operating systems therefor for use in pumping fluids from boreholes, and especially an oil well production system for stripper wells wherein crude oil is removed from the borehole as fast as it comes into the well. This system includes weight indicators, downhole sensing devices, including fluid level detecting devices, bottom hole pressure measurement, detection of oil/water contact or interface, and a cable actuated downhole production pump that can handle both oil and gas. All of these system parts are assembled and programmed to operate a novel downhole production pump at a production rate equal to the flow rate of the produced oil flowing into the well bore from the casing perforations. This keeps the hydrostatic head at the perforations at a minimum value which can be substantially zero, so that the downhole hydrostatic pressure imposed on the production zone is relatively low, which is a condition that achieves maximum production of oil from an oil well.
Reduced power consumption is realized by the incorporation of a very long pump barrel having a special cable actuated lifting plunger received therein that is slowly reciprocated uphole and then lowered back into the well 24 hours per day. This novel lifting system is designed for maximum efficiency as well as increased recovery of oil from old stripper wells; especially old wells that have declined in yearly production to only 10 barrels of oil per day or less, for example, when using conventional pump systems. Properly installed, the system set forth in this disclosure could significantly increase present production in old stripper wells while at the same time reducing the cost of operation.
Sensing devices are employed to control the action of the production apparatus which enables the speed of the operation to be controlled to match the rate of fluid input into the well bore at the casing perforations, thereby saving energy by allowing the pump to operate in a timed cyclic mode which upstrokes after there is a predetermined accumulation of production fluid in the pump barrel ready to be removed from the bottom of the borehole.
Accordingly, each time the operating cable is lowered into the borehole, diagnosis by the surface equipment determines the downhole fluid level, and, when there is less than a full pump barrel of formation fluid available to be transferred into the pump barrel, the timing of the next operating cycle is modified to coincide with the formation production rate so that a full pump barrel is attained prior to each upstroke. This additional cycle time provides sufficient time for the well to make the additional fluid needed to completely fill the pump barrel with the accumulated well fluid and further keeps a minimum hydrostatic head at the perforations.
Many unprofitable stripper wells can be operated profitably by judiciously diagnosing the operating history of the well and carrying out any future operation of the well in accordance with this invention.
Therefore, a primary object of the present invention is the provision of both method and apparatus of a pump system made in accordance with this disclosure that employs a cyclicly continuously operated slow moving, long stroking plunger on the upstroke and on the downstroke to save power by moving a relatively large column of fluid uphole each upstroke of the plunger as contrasted to a short stroking pump, such as a pumpjack, which has a fast moving short stroking plunger on both the upstroke and downstroke.
Another object of the present invention is the provision of a cable actuated downhole pump assembly that forces an unusual quantity of fluid uphole on the upstroke while overcoming inertia one time instead of several times for the same quantity of production fluid.
A further object of the present invention is the provision of a cable actuated downhole pump assembly that easily can be pulled for servicing by reeling or spooling the lifting cable uphole until the pump barrel surfaces and then, after changing out various parts, the pump easily is run back into the hole on the operating cable; thus avoiding the necessary expense of using a pulling unit.
Another and still further object of this invention is the provision of a downhole pump assembly having a unique bypass valve device that is opened in response to the pump barrel initially being lifted uphole by the operating cable and thereby equalizes the pressure between the tubing and the casing annulus, and also washes debris from the lower end of the pump assembly in proximity of the hold-down, all of which avoids a stuck pump.
A still further object of the present invention is the provision of a downhole pump assembly having a plurality of sensor devices uniquely connected to an uphole controller to monitor the pumping operation and enable selection of the optimum time intervals for making a relative slow upstroke, followed by a downstroke of another timed interval; with this cyclic operation being modified by the controller each cycle of operation to maintain a continuous optimum production as conditions change.
A still further object of the invention is a pumping system that skims oil from a hydrocarbon producing well by allowing the pump plunger to descend through the oil phase in the pump barrel and stop at the oil/water interface, thereby producing or skimming hydrocarbons (oil and gas) without producing excessive water.
A still further object of the present invention is the provision of a downhole pump assembly operated in a manner to keep the hydrostatic head in front of each perforation at a minimum so that the fluid from the pay zone is free to flow into the wellbore without being held back by an excessive fluid hydrostatic head.
A still further object of the present invention is the provision of a downhole pump assembly operated in a manner whereby compressible fluid produced by the pay zone is admixed with liquid rather than vented up the casing string, and the mixed fluids are passed through the pumping chamber, and up the production tubing each upstroke of the pump.
A still further object of the present invention is the provision of a downhole pump assembly operated in a manner whereby fluid is pumped to the surface at the same rate that fluid is produced from a formation within a time interval of one cycle of operation calculated from stored data related to the production history of the well to determine the quantity of fluid contained within the pump each cycle of operation and to change the time interval for successive cycles of operation so as to continually adjust the time intervals to coincide with the rate of production of the formation whereby the optimum rate of production is attained and the cyclic operation continues until the well is shut down.
Another and still further object of this invention is the provision of a downhole pump assembly operated in a manner whereby there is no danger of fluid pounding, even though the well is always operated under severe pump-off conditions, because the gas ingested by the pump is slowly expelled up the production tubing each pump upstroke, and thereby enhances pumping efficiency.
A still further object of the invention is a pumping system that skims oil from a hydrocarbon producing well by allowing the pump plunger to descend through the oil phase in the pump barrel and stop adjacent the oil/water interface, thereby producing or skimming hydrocarbons (oil and gas) without producing excessive water, while the formation gas is flowed into the working chamber, and is expelled from an upper stationary valve with the production rate being held to a value that keeps the hydrostatic head in front of each perforation at a minimum so that the fluid from the pay zone is free to flow into the wellbore without being held back by an excessive fluid hydrostatic head.
A still further object of the present invention is the provision of a downhole pump assembly operated in a manner whereby compressible fluid produced by the pay zone is admixed with liquid and the mixed fluids are passed through the pumping chamber, and up the production tubing each upstroke of the pump assembly and becomes part of the fluid contained within the production tubing, thereby reducing the tubing hydrostatic pressure or fluid density and enhancing lift in a manner similar to a gas lift well.
A still further object of the present invention is the provision of a downhole pump assembly operated in a manner whereby the simplicity of design is reflected in lower initial cost and subsequent low operation maintenance, which, together with the enhanced production of the well, makes a marginal well into a profitable one.
These and various other objects and advantages of the invention will become readily apparent to those skilled in the art upon reading the following detailed description and claims and by referring to the accompanying drawings.
These and other objects are attained in accordance with the present invention by the provision of a method for use with apparatus fabricated and operated in a manner substantially as described herein.